In a known potentiometer of this type, a mechanical multidigit counter is mounted outside the potentiometer housing on the shaft carrying the slider. The counter is coupled to the shaft of the potentiometer and provides a direct digital indication of the angular position of the shaft. Digital displays of this type are usually employed on multi-turn potentiometers in which the position of the slider is difficult to determine from the outside.
There are a number of disadvantages which are typical of potentiometers of this type. Since the counter is mounted on the potentiometer shaft proper, the potentiometer must be mounted in an apparatus at a point at which the counter can be read. This means that normally the potentiometer must be mounted on the front plate of the instrument. This is a considerable restriction in regard to the configuration of the circuit elements.
Another disadvantage of the known potentiometer results from the fact that restrictions exist for the scale of the counter. Unless a counter especially designed for a particular potentiometer is used, one must be satisfied with a total slider path length corresponding to a co-nter position of, say, 897 scale divisions. It is usually desirable to relate an even number such as 1000 to the total path length of the slider